The present invention relates to an intravenous (IV) infusion device. More particularly, the present invention relates to an automatic clamp for controlling flow rate of IV fluid in an infusion device.
Infusion devices are used to deliver IV fluids to patients. A typical infusion device includes a fluid source or reservoir, a drip chamber and an IV tube set. Fluid drips from the reservoir through the drip chamber into the IV tube. The rate at which the fluid drips from the fluid reservoir is proportional to the flow rate of the fluid through the IV tube.
Physicians often require IV fluid to be delivered to patients at a certain rate. Therefore, it is necessary to control the flow rate of the IV fluid through the IV tube.
In the past, flow rate controllers were developed which used electromechanical devices to apply a pinching force to the IV tube. By pinching the IV tube, the flow of IV fluid through the IV tube was restricted and the flow rate was controlled. The degree of flow restriction varied based on a feedback system.
However, typical IV tubes are formed of a material having a certain resilience. Most of the pinching force required to restrict flow of IV fluid through the IV tube is needed to overcome the resilience of the IV tube. Therefore, an IV controller requires a large amount of electrical energy to drive the electromechanical pinching device. This is especially true where the pinching device is used with a standard set of IV tubes because of the stiffness of the IV tubes. For an IV controller of this type to be provided with an adequate amount of electrical energy, it must either by connected to an AC source or have a large battery. In either case, this type of IV device is not a practical device to be used with ambulatory patients.
For these reasons, there have been several attempts to provide the medical community with an IV control device that is small and that contains its own power source. One example is the Danby U.S. Pat. No. 4,533,350 which utilizes a battery for control power. In order to keep the power requirements of the controller low, a special IV tube set having a special control valve is used. The special IV tube set is designed to decrease the amount of pinching force required to restrict flow in the IV tube in order to achieve a corresponding decrease in the power requirements of the controller.
Similarly, the Krumme U.S. Pat. No. 4,645,489 illustrates an attempt to provide a small IV control device with self-contained energy requirements. The device in Krumme uses a shaped memory alloy driven by electrical energy to provide the pinching force. However, as with Danby, the Krumme patent requires a special IV tube set to reduce the required pinching force.
Because of the special IV tube sets required in both the Danby and Krumme patents, the cost of the IV device is higher than it would be if a standard IV tube set were used. Additionally, this extra cost is recurring each time the device is used since a new IV tube set is required for each infusion.
Another technique for controlling the flow of fluid in an IV tube involves a simple mechanical clamp. The flow rate through the IV tube is initially set by an attending medical person observing the drip rate in the drip chamber. The clamp is adjusted to maintain a set flow rate. Periodically, the attending medical person returns to the IV set, monitors the flow rate and adjusts the mechanical clamp. There is no automatic feedback system for variably controlling the clamp to adjust the flow rate to compensate for deviations caused by varying environmental conditions such as hydrostatic pressure or venous pressure. Hence, the technique is inefficient because of the time required by the attending medical person to periodically monitor and adjust the mechanical clamp. In addition, this technique requires the attending medical person to make an accurate determination of the flow rate each time the mechanical clamp is adjusted. Therefore, errors are likely.
Spring power has been used in the past to propel the IV fluid from the reservoir. For example, the Brown U.S. Pat. No. 4,741,736 teaches a programmable infusion pump which has a constant force spring to force the fluid from the reservoir. However, flow restriction is controlled by a mechanical screw clamp which is not automatically variable.
Other spring power propulsion devices are taught by the Muller U.S. Pat. No. 3,384,080; the Hargest U.S. Pat. No. 3,647,117; the Hill U.S. Pat. No. 3,670,926 and the Sealfon U.S. Pat. No. 4,447,232. All of these devices teach the use of spring driven pumps to force the IV fluid from the reservoir.
Another major power requirement for past electromechanical IV clamps, in addition to overcoming the tube resilience in flow rate control, is the requirement of setting an initial flow rate. In past electromechanical flow rate controllers, an operator would insert the IV tube into the flow rate controller and enter a desired initial flow rate through, for example, a keypad entry system. Then, the electromechanical flow rate controller would drive a pinching device until the initial flow rate was achieved. This would sometimes require electromechanically driving the pinching device a relatively large distance, thus resulting in a large amount of power consumption during this phase of operation.